Can I Use Dirty Gravel for a Retaining Wall?

Application

• In order to build a stable, long-lasting retaining wall, you must first lay a solid base. Once growth is cleared, a trench equal in width to half the height of the wall should be excavated and compacted. Instead of laying down a gravel and mortar base, pour a 4-inch-thick layer of dirty gravel over the trench and pound it down with the tamper. Moisten the surface so the stone dust hardens between any gaps in the rocks, binding them like cement.

Backfill

• One of the final steps to constructing a retaining wall is to line the back with a 12-inch-wide layer of gravel backfill. This gravel must be clean so that underground moisture can seep through the cracks and down into a drain system beneath the wall. If you use dirty gravel, the dense material will force water pressure to build up and eventually threaten the stability of the wall.

Advantages

• Dirty gravel offers a number of advantages for do-it-yourselfers. Once mortar is mixed and spread, it begins to harden quickly. This creates time pressure that prevents you from properly installing the first course of stones or bricks, and an uneven first course can throw off the look and structural integrity of the whole wall. Unlike mortar, you can take your time when building a base with dirty gravel to make sure that it’s done right. This material is also affordable and easy for novices to use.

Considerations

• The composition of dirty gravel varies by region and quarries, and can include clay, dirt, small shale gravel and stone dust. Typically, dirty gravel is messy to work with and releases dust when poured. If dirty gravel is exposed to fast-moving water, the fines in the mix can wash away and destabilize the gravel if it's not compacted well. Spray dirty gravel with water to limit dust, and wear a face mask to protect yourself from breathing in dust.